WIP - adding dart fix support to the engine (dart:ui)

[Piinks]

Not sure if dart fix will support dart:X but let's see... following up in dart-lang/sdk#59764

Would fix #160617

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[matanlurey]

This isn't a "real" package, so I doubt this will work as expected :-/

(Could we put the fixes in packages/flutter instead of in the engine, possibly?)

[Piinks]

(Could we put the fixes in packages/flutter instead of in the engine, possibly?)

Would definitely prefer that!

@bwilkerson just shared in dart-lang/sdk#59764:

So the right answer here is probably to have a second place to look for fixes related to dart: libraries.

If so, we should be able to choose where that is!

[matanlurey]

Cool - I'm happy to review (I didn't make most of the Color changes but I'm pretty familiar with them)

[Piinks]

Closing as it is currently blocked on dart-lang/sdk#59764